1. Field of the Invention
The present invention relates generally to fiber processing plants and, more particularly, to an emission control system and method for controlling the amount of airborne particulate matter in the fiber-containing airflow discharging from the fiber processing plant.
2. Related Art
Fiber processing plants typically produce one or more fiber-containing airflows discharging from one or more machines used to process the fiber, which may be natural or synthetic. In some instances, this fiber-containing airflow is discharged to the environment surrounding the plant, while in other instances it is recycled to the interior of the plant. In either case, it is important to control the amount of particulate matter within the fiber-containing airflow, either for environmental considerations exterior of the plant or for health considerations with respect to the workers within the plant. The weight flowrate of the particulate matter within the fiber-containing airflow may be relatively high and accordingly, control of this airborne pollution has been an ongoing concern.
Various devices and methods have been used to control the airborne pollution discharging from fiber processing plants. For instance, cotton gins have typically used a plurality of devices known as cyclones to separate at least a portion of the particulate matter from the fiber-containing airflows discharging from the cotton gin. Cotton gins typically include a network of pipes or conduits which are used to transport the cotton from one processing machine to another within the plant, as a result of the pressure of the airflow within the pipes. The fiber processing devices within a cotton gin typically include at least one ginning stand which is used to remove the cotton seeds, a feed control device, an incline, one or more dryers, a plurality of lint cleaners or separators and one or more cotton balers. Several of these fiber processing devices, such as each of the separators, typically communicate with a pipe containing an exhaust fan. The system of exhaust pipes and fans are used to create the required suction to transport the cotton from one station to another and to perform the required processing within a particular device.
Due to the nature of the processing within the particular fiber processing device, the airflow within the corresponding exhaust pipe may include relatively small fibers of cotton and other particulate matter such as particles of leaves from the cotton plant or other debris. For instance, a lint cleaner or separator typically includes an internal, screen drum, with the interior of this drum communicating with the exhaust pipe. The screen mesh is too small to permit the relatively large cotton staple to pass through the screen, but is small enough to permit relatively small pieces of cotton lint, pieces of cotton plant leaves or other debris to pass through the screen and into the exhaust pipe. Each of these exhaust pipes, which are used to transport the fiber-containing airflow, is coupled to a cyclone where the airflow is directed tangentially into an upper portion of the cyclone. As a result of the tangential entry into the cyclone, the fiber-containing airflow spirals downward along the inner wall of the cyclone. At the bottom of the lower, conical portion of the cyclone, the air reverses direction and spirals up the center of the cyclone, exhausting to atmosphere through a centrally disposed vent tube and an upper, outlet opening in the cyclone. At the point of air direction reversal, a large portion of the particulate matter, or trash, being conveyed in the airflow precipitates out the bottom of the cyclone and is deposited onto the ground or alternatively onto a collection device such as the bed of a truck. The remainder of the particulate matter discharges through the top vent opening of the cyclone directly into the atmosphere without being collected. This creates a "cloud" of particulate matter surrounding the cyclone which is a source of airborne pollution. The amount of particulate matter deposited on the ground, as compared to the amount which remains airborne, depends on the efficiency of the cyclone. The allowable emissions from a cotton gin may vary with process weight rate, as stipulated by environmental control regulations. For instance, a cotton gin having a process weight rate of 14,000 lbs/hr may have a permissible rate of airborne emissions of about 15 lbs/hr, which results in a substantial amount of airborne pollution. This problem may be exacerbated by the use of cyclones as an emission control device, since a portion of the airflow discharges through the lower outlet port of the cyclone at a relatively high velocity as it impacts the particulate matter lying on the ground or the collection device, which adds to the cloud of airborne pollution surrounding the cyclone.
Mote plants, which are used to process lower grades of cotton containing a significant amount of debris, provide another example of cotton processing plants which utilize the previously described cyclones. Although the governing environmental regulations may impose a much stricter limit on the airborne particulate matter discharging from mote plants, for instance 6.0 lbs/hr in some areas, these plants may still generate a significant amount of airborne pollution.
Another disadvantage associated with the use of cyclones, when trucks or other motorized vehicles are used to collect or transport the pile of trash precipitated from the fiber-containing airflow, is the adverse affect on the operation and maintenance of the trucks or other vehicles. For instance, the small fibers of cotton and other particulate matter tend to collect on various parts of the vehicle, including the engine, battery and radiator, which has been known to cause vehicle fires or overheating resulting in serious damage to the vehicle.
Historically, cotton gins and other cotton processing plants have been located in rural areas having a relatively low density of both commercial and residential homes. However, an increasing number of these areas are being developed with respect to both commercial and residential structures, which increases the need for improved methods of controlling the airborne pollution emanating from cotton gins and other cotton processing plants. Over the years, as the population has expanded toward the rural areas, some cotton gins have been forced out of business due to environmental considerations.
Other known air cleaning or emission control systems associated with fiber processing plants may include rotating machinery and/or other pieces of relatively complex machinery. For instance, known air cleaning systems associated with textile mills may include a motorized sweep mechanism to remove the fibers and other particulate matter collected on a screen-covered drum after a fiber-containing airflow has passed through the drum, and an auger or screw conveyor to transport the fibers and other particulate matter to a collection area. While these systems may be advantageously used with regard to emission control, the included equipment is relatively complex and may have relatively high purchase and maintenance costs.
In view of the foregoing deficiencies associated with known devices and methods for controlling the airborne pollution discharging from fiber processing plants, there remains a need for a simple, economic and efficient emission control system and method for controlling the particulate matter discharging from a fiber processing plant.